1. Field of the Invention
The present invention relates to construction machinery, and particularly to a concrete placing apparatus. The invention is applicable in the building industry for casting solid concrete and reinforced concrete walls.
2. Description of the Prior Art
There is known a variety of formworks which are used for casting solid walls. The USSR Author's Certificate No. N 224032 (Int. Cl. E04G 11/12) describes a collapsible formwork which comprises jacks, formwork boarding mounted on both sides of the wall being cast, and U-shaped frames suspended on the jacks and provided with rollers to move on the formwork boarding.
Erecting a wall with the aid of such formwork is effected as follows. The concrete mix is poured into the formwork, and lifting the frames with the working deck as the wall grows in height, the lower part of formwork boarding is dismantled and mounted over the upper end of the formwork.
However, using the above collapsible formwork necessitates alternate dismantling and mounting the formwork boording during the whole operation, which entails increased consumption of labour and time.
Higher efficiency can be achieved with the aid of a sliding formwork (cf. "Opalubka," Politechnicheskiy Slovar, Moskwa, "Sowetskaya Encyclopedia," 1978, p. 328). The formwork of this type generally comprises the same elements as the formwork described above.
The U-shaped frames in this sliding formwork are not provided with rollers, and the formwork boarding is rigidly attached to the frames. In this case the formwork is lifted together with the frames, thereby providing for continuous casting of the wall. This type of formwork also has a number of disadvantages. First, this formwork is mounted along the whole length of the wall being erected and in the case of large walls, is large and heavy, thus complicating the whole concrete placing operation. It should also be noted that with the increase of length of the formwork boarding the amount of friction between the latter and the concrete also increases. Second, the above formwork, does not permit casting a wall with variable cross-section, and in particular is not adapted for producing offsets on the walls for the floor slabs or relieving slabs in the case of retaining walls to rest on. Third, this formwork doesn't permit erecting a wall using two different concrete compositions simultaneously, for example, a wall wherein the face side is made from the high-grade concrete and the back side from the low-grade concrete, or from light-weight and heavy-weight concretes respectively. This formwork does not permit, for the same reason, casting a wall with the face and back sides having different colours. Due to all these reasons the above formwork cannot provide savings either in labour or in materials.
For erecting solid concrete walls there are also used concrete placing apparatus, which provide for speeding up the erection operation. The USSR Author's Certificate No. N 654,786 describes a concrete placing apparatus for casting solid walls, permitting most of the difficulties associated with the above formworks to be overcome.
This concrete placing apparatus comprises jacks arranged in line along the wall being cast, U-shaped frames mounted on these jacks and connected with each other by means of scaffolds positioned along and on both sides of the line of arrangement of the jacks, and driving carriages mounted on these scaffolds for movement therealong, and carrying each a feed hopper, a moulding board and a concrete compacting means.
The concrete compacting means is a surface vibrator disposed behind the feed hopper and adapted for compacting freshly placed concrete.
The presence of carriages in this apparatus makes unnecessary using long moulding boards in the case of long walls, thus decreasing the size and weight of the apparatus.
Furthermore, owing to the presence of several feed hoopers mounted on the carriages positioned on both sides of the wall, the latter can be cast using two different concrete mixes simultaneously.
This concrete placing apparatus, however, also has a number of disadvantages. For example, it does not permit casing a wall with a variable cross section. In addition, the surface-type vibrators, which compact the concrete mix by impacting it after it has been placed, excite vibration of the previously placed concrete, thus preventing the latter from rapid setting, and thereby slowing down the operation.